Cutting inserts for a milling cutter are mounted onto a plurality of pockets formed in a milling cutter body. Each of the cutting inserts is fixed to each pocket by means of a clamp screw inserted into a screw-hole formed in the central portion of the cutting insert. Such cutting inserts are subject to a rotational torque by the reaction from the workpiece during the cutting process. If the cutting insert is shaped to be polygonal (e.g., triangle, square, etc.), then the cutting insert cannot be rotated, although such a rotational torque is applied. This is because the side surface of the cutting insert is mated with the mounting wall formed in the pocket. However, if the cutting insert is shaped to be circular, then the cutting insert may be rotated and thrown away from the pocket, although the side surface and the receiving wall of the pocket are mated with each other.
In order to solve the above problem, a cutting insert (10) of prior art comprises a plurality of recesses (12) on the lower side surface or a bottom surface of the cutting insert (10) as shown in FIG. 1. Further, a pocket (20) of the milling cutter in which the cutting insert (10) is seated is provided with protrusions (14) for being mated with the recesses (12) of the cutting insert (10) as shown in Fig 2. Accordingly, the cutting insert was prevented from rotating during the cutting process. However, since such a cutting insert (10) may be operated as only a single-sided insert, it was not economical. Also, the side surface portion of the cutting insert (10), which is mated with the protrusions (14) of the pocket, is limited to only the lower surface in which the recesses (12) are formed. Thus, a broad mounting area between the cutting insert (10) and the pocket (20) was not ensured. Accordingly, the cutting insert cannot be stably mounted.
A double-sided cutting insert (30), which prevents a rotation during the cutting process, is disclosed in U.S. Pat. No. 6,607,335 (see FIGS. 3 and ). The cutting insert (30) comprises contact surfaces (32, 32′) symmetrically formed in the upper and lower directions and formed in the circumferential direction of the side surface. One of the top contact surface and bottom contact surface (32 or 32′) is mated with the tool body (40) to prevent the rotation of the cutting insert. However, since only one of the contact surfaces (32, 32′) is mated with the tool body, the mounting area between the cutting insert (30) and the tool body (40) cannot be broad as in the previous case.